<!DOCTYPE html>
<html>
	<head>
	<meta charset="utf-8">
		<title>Insert title here</title>
		<link rel="stylesheet" href="css/display_visibility.css">
	</head>
	<body>
		<h1>This a headline...</h1>
		<h1 class="display_none">This a headline...</h1>
		<h1 class="hidden">This a headline...</h1>
		<h1>This a headline...</h1>
		<p>(X<sub>1</sub><sup>2</sup>+X<sub>2</sub><sup>2</sup>)<sup>2</sup></p>
	</body>
</html>